Conventional articles of footwear, e.g., athletic footwear, have included two primary elements, namely an upper member and a sole member. The upper member and the sole member, at least in part, define a foot-receiving chamber that may be accessed by a user's foot through a foot-receiving opening. The upper member provides a covering for the foot that securely receives and positions the foot with respect to the sole member. The upper member may extend around the ankle, over the instep and toe areas of the foot, along the medial and lateral sides of the foot, and around the heel area of the foot. In addition, the upper member may have a configuration that protects the foot and provides ventilation, thereby cooling the foot and removing perspiration.
The sole member generally is secured to a lower portion of the upper member and generally is positioned between the foot and the contact surface (any foot or footwear contact surface, including but not limited to: grass, dirt, snow, ice, tile, flooring, carpeting, synthetic grass, and the like). In addition to attenuating ground reaction forces, the sole member may provide traction and help control foot motion, such as excess pronation. Accordingly, the upper member and the sole members may operate cooperatively to provide a comfortable structure that is suited for a variety of ambulatory activities, such as walking and running.
The sole member of an article of footwear, in at least some instances, will exhibit a layered configuration that includes a comfort-enhancing insole, a resilient midsole (e.g., formed, at least in part, from a polymer foam material), and a surface-contacting outsole that provides both abrasion-resistance and traction. Suitable polymer foam materials for the midsole member include ethylvinylacetate (“EVA”) or polyurethane (“PU”) that compress resiliently under an applied load to attenuate ground reaction forces. Conventional polymer foam materials are resiliently compressible, in part, due to the inclusion of a plurality of open or closed cells that define an inner volume substantially displaced by gas.